System and method for detecting operating events of an engine

ABSTRACT

A method of monitoring an operating event of a combustion engine includes receiving a noise signal sensed by a knock sensor disposed in or proximate to the combustion engine, correlating the noise signal with a fingerprint having at least an ADSR envelope indicative of the operating event, and detecting if the operating event has occurred based on the correlating of the noise signal with the fingerprint.

The subject matter disclosed herein relates to fuel combusting enginesand, more specifically, to a system and method for detecting operatingevents and conditions of a reciprocating engine using a knock sensor.

Combustion engines typically combust a carbonaceous fuel, such asnatural gas, gasoline, diesel, and the like, and use the correspondingexpansion of high temperature and pressure gases to apply a force tocertain components of the engine, e.g., piston disposed in a cylinder,to move the components over a distance. Each cylinder may include one ormore valves that open and close correlative with combustion of thecarbonaceous fuel. For example, an intake valve may direct an oxidizersuch as air into the cylinder, which is then mixed with fuel andcombusted. Combustion fluids, e.g., hot gases, may then be directed toexit the cylinder via an exhaust valve. Accordingly, the carbonaceousfuel is transformed into mechanical motion, useful in driving a load(e.g., a generator that produces electric power). In traditionalconfigurations, timing of opening and closing the intake and exhaustvalves during operation of the combustion engine may be monitored andestimated using traditional techniques. Traditional techniques may alsobe used for detecting certain other operating events and conditions(e.g., peak firing pressure) of the combustion engine. However,traditional monitoring techniques may not be accurate, and correctivemeasures utilizing the traditional monitoring techniques may reduce anefficiency of the internal combustion engine. Accordingly, improvedmonitoring of operating events and conditions, such as peak firingpressure and/or intake and exhaust valve closure (or opening) operatingevents, may be useful.

BRIEF DESCRIPTION

Certain embodiments commensurate in scope with the originally claimedinvention are summarized below. These embodiments are not intended tolimit the scope of the claimed invention, but rather these embodimentsare intended only to provide a brief summary of possible forms of thepresent disclosure. Indeed, the present disclosure may encompass avariety of forms that may be similar to or different from theembodiments set forth below.

In a first embodiment, a method of monitoring an operating event of acombustion engine includes receiving a noise signal sensed by a knocksensor disposed in or proximate to the combustion engine, correlatingthe noise signal with a fingerprint having at least an ADSR envelopeindicative of the operating event, and detecting if the operating eventhas occurred based on the correlating of the noise signal with thefingerprint.

In a second embodiment, a system includes an engine controllerconfigured to monitor a first operating event of a combustion engine.The controller includes a processor configured receive a noise signalsensed by a knock sensor disposed in or proximate to the combustionengine, correlate the noise signal with a first fingerprint having atleast a first ADSR envelope indicative of the first operating event, anddetect if the operating event has occurred based on the correlating ofthe noise signal with the first fingerprint.

In a third embodiment, a non-transitory computer readable mediumincludes executable instructions that, when executed, cause a processorto receive, from a knock sensor disposed in or proximate to an internalcombustion engine, noise data indicative of noise emitted by theinternal combustion engine. The executable instructions, when executed,also cause the processor to receive, from a crankshaft sensor disposedin or proximate to the combustion engine, crank angle data indicative ofa crank angle of a crankshaft of the internal combustion engine.Further, the executable instructions, when executed, cause the processorto plot the noise data against the crank angle data, determine a portionof the noise data that corresponds to a fingerprint having a referenceADSR envelope indicative of an operating event of the internalcombustion engine, superimpose the reference ADSR envelope over theportion of the noise data, and determine a location in the noise data atwhich the operating event occurred.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of an embodiment of a portion of an enginedriven power generation system in accordance with aspects of the presentdisclosure;

FIG. 2 is a side cross-sectional view of an embodiment of a pistonassembly within a cylinder of the reciprocating engine shown in FIG. 1in accordance with aspects of the present disclosure;

FIG. 3 is an embodiment of an engine noise plot of data measured by theknock sensor shown in FIG. 2 in accordance with aspects of the presentdisclosure;

FIG. 4 is an embodiment of a scaled version of the sample engine noiseplot shown in FIG. 3 in accordance with aspects of the presentdisclosure;

FIG. 5 is an embodiment of a sample scaled engine noise plot shown inFIG. 4 with four principle parameters of an attack, decay, sustain,release (ADSR) envelope overlaid in accordance with aspects of thepresent disclosure;

FIG. 6 is an embodiment of a scaled engine noise plot and ADSR envelopeshown in FIG. 5 with the extracted tones overlaid in accordance withaspects of the present disclosure;

FIG. 7 is a flow chart showing an embodiment of a process forcharacterizing a noise in accordance with aspects of the presentdisclosure;

FIG. 8 is a an embodiment of a scaled engine noise plot corresponding toan engine operating event, an operating event indicator corresponding tothe engine operating event, and an ADSR envelope corresponding to theengine operating event in accordance with the process of FIG. 7 andother aspects of the present disclosure;

FIG. 9 is a flow chart showing an embodiment of a process foridentifying a fingerprint shown in FIG. 7 in accordance with aspects ofthe present disclosure; and

FIG. 10 is a flow chart of an embodiment of a process suitable forprocessing engine noise to derive certain engine operating events.

DETAILED DESCRIPTION

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

The disclosed embodiments employ sensors (e.g., knock sensors, acousticsensors, or vibration sensors) and baseline data (e.g., fingerprints ofsound or vibration) to monitor, diagnose, and/or control an engine. Whenusing a knock sensor to monitor a combustion engine, occasionally theknock sensor system records a noise, such as an abnormal or undesirednoise that may not be identified at that time. Alternatively, the knocksensor may record a noise that is a normal or desired noise, where thenoise has been previously identified and characterized. For example,noises emitted by the combustion engine during various actions by thecombustion engine may be initially characterized during an in-factorybaselining process. Noise signals for particular operating events andconditions (e.g., valve closures, valve openings, and peak firingpressure) during the baselining process may be processed and stored in adatabase as relating to one or more operating events. During normaloperation of the combustion engine, data stored in the database relatingto the operating events characterized during the baselining process maybe accessed to determine if operational noise corresponds to theoperating events characterized during the baselining process.

Advantageously, the techniques described herein may create a sound“fingerprint” of certain engine sounds or noise. The fingerprint (e.g.,profile, comparator, and/or reference signal) may be developed duringthe baselining process, as described above, and the fingerprint maycorrespond to a particular operating event (e.g., a valve closure)tested during the baselining process. It should be noted that thebaselining process may be carried out during full operation of thecombustion engine or while only operating certain components (e.g., thecomponents relating to the operating event(s) being baselined) of thecombustion engine. For example, in some embodiments, various operatingevents of the combustion engine may be baselined in-factory during partor full operation.

During full operation of the combustion engine (e.g., after baselining),noise may be detected by the knock sensor, and the noise signal may beprocessed and compared to various fingerprints (e.g., profiles,signatures, comparators, reference signals, unique indicia, uniquerepresentations, etc.) relating to the combustion engine. If thefingerprint and the processed noise signal correspond or correlate(e.g., “match”), the signal may be confirmed as corresponding to theoperating event relating to the fingerprint. The noise signal may alsobe processed to determine time-sensitive information relating to theoperating event that corresponds to the matched fingerprint and noisesignal. For example, if the noise signal matches a fingerprintcorresponding to closure of an exhaust valve, the noise signal may beplotted with respect to time (or crank angle) to determine when theexhaust valve closed.

As described in further detail below, systems and method are providedfor identifying and classifying noise via anAttack-Decay-Sustain-Release (ADSR) envelope and/or joint time-frequencytechniques, where the ADSR envelope may correspond to at least a portionof the above-referenced fingerprint. The joint time-frequency techniquesmay include cepstrum techniques, quefrency techniques, chirplettechniques, and/or wavelet techniques to develop an acoustic model orfingerprint of the noise, as described in more detail below.

Turning to the drawings, FIG. 1 illustrates a block diagram of anembodiment of a portion of an engine driven power generation system 8.As described in detail below, the system 8 includes an engine 10 (e.g.,a reciprocating internal combustion engine) having one or morecombustion chambers 12 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16,18, 20, or more combustion chambers 12). An air supply 14 is configuredto provide a pressurized oxidant 16, such as air, oxygen,oxygen-enriched air, oxygen-reduced air, or any combination thereof, toeach combustion chamber 12. The combustion chamber 12 is also configuredto receive a fuel 18 (e.g., a liquid and/or gaseous fuel) from a fuelsupply 19, and a fuel-air mixture ignites and combusts within eachcombustion chamber 12. The hot pressurized combustion gases cause apiston 20 adjacent to each combustion chamber 12 to move linearly withina cylinder 26 and convert pressure exerted by the gases into a rotatingmotion, which causes a shaft 22 to rotate. Further, the shaft 22 may becoupled to a load 24, which is powered via rotation of the shaft 22. Forexample, the load 24 may be any suitable device that may generate powervia the rotational output of the system 10, such as an electricalgenerator. Additionally, although the following discussion refers to airas the oxidant 16, any suitable oxidant may be used with the disclosedembodiments. Similarly, the fuel 18 may be any suitable gaseous fuel,such as natural gas, associated petroleum gas, propane, biogas, sewagegas, landfill gas, coal mine gas, for example.

The system 8 disclosed herein may be adapted for use in stationaryapplications (e.g., in industrial power generating engines) or in mobileapplications (e.g., in cars or aircraft). The engine 10 may be atwo-stroke engine, three-stroke engine, four-stroke engine, five-strokeengine, or six-stroke engine. The engine 10 may also include any numberof combustion chambers 12, pistons 20, and associated cylinders (e.g.,1-24). For example, in certain embodiments, the system 8 may include alarge-scale industrial reciprocating engine having 4, 6, 8, 10, 16, 24or more pistons 20 reciprocating in cylinders. In some such cases, thecylinders and/or the pistons 20 may have a diameter of betweenapproximately 13.5-34 centimeters (cm). In some embodiments, thecylinders and/or the pistons 20 may have a diameter of betweenapproximately 10-40 cm, 15-25 cm, or about 15 cm. The system 10 maygenerate power ranging from 10 kW to 10 MW. In some embodiments, theengine 10 may operate at less than approximately 1800 revolutions perminute (RPM). In some embodiments, the engine 10 may operate at lessthan approximately 2000 RPM, 1900 RPM, 1700 RPM, 1600 RPM, 1500 RPM,1400 RPM, 1300 RPM, 1200 RPM, 1000 RPM, 900 RPM, or 750 RPM. In someembodiments, the engine 10 may operate between approximately 750-2000RPM, 900-1800 RPM, or 1000-1600 RPM. In some embodiments, the engine 10may operate at approximately 1800 RPM, 1500 RPM, 1200 RPM, 1000 RPM, or900 RPM. Exemplary engines 10 may include General Electric Company'sJenbacher Engines (e.g., Jenbacher Type 2, Type 3, Type 4, Type 6 orJ920 FleXtra) or Waukesha Engines (e.g., Waukesha VGF, VHP, APG, 275GL),for example.

The driven power generation system 8 may include one or more knocksensors 23 suitable for detecting engine “knock.” The knock sensor 23may be any sensor configured to sense sounds or vibrations caused by theengine 10, such as sound or vibration due to detonation, pre-ignition,and or pinging. The knock sensor 23 is shown communicatively coupled toan engine control unit (ECU) 25. During operations, signals from theknock sensor 23 are communicated to the ECU 25 to determine if knockingconditions (e.g., pinging) exist. The ECU 25 may then adjust certainengine 10 parameters to ameliorate or eliminate the knocking conditions.For example, the ECU 25 may adjust ignition timing and/or adjust boostpressure to eliminate the knocking. As further described herein, theknock sensor 23 may additionally derive that certain sounds orvibrations should be further analyzed and categorized to detect, forexample, undesired engine conditions.

FIG. 2 is a side cross-sectional view of an embodiment of a pistonassembly 25 having a piston 20 disposed within a cylinder 26 (e.g., anengine cylinder) of the reciprocating engine 10. The cylinder 26 has aninner annular wall 28 defining a cylindrical cavity 30 (e.g., bore). Thepiston 20 may be defined by an axial axis or direction 34, a radial axisor direction 36, and a circumferential axis or direction 38. The piston20 includes a top portion 40 (e.g., a top land). The top portion 40generally blocks the fuel 18 and the air 16, or a fuel-air mixture 32,from escaping from the combustion chamber 12 during reciprocating motionof the piston 20.

As shown, the piston 20 is attached to a crankshaft 54 via a connectingrod 56 and a pin 58. The crankshaft 54 translates the reciprocatinglinear motion of the piston 24 into a rotating motion. As the piston 20moves, the crankshaft 54 rotates to power the load 24 (shown in FIG. 1),as discussed above. As shown, the combustion chamber 12 is positionedadjacent to the top land 40 of the piston 24. A fuel injector 60provides the fuel 18 to the combustion chamber 12, and an intake valve62 controls the delivery of air 16 to the combustion chamber 12. Anexhaust valve 64 controls discharge of exhaust from the engine 10.However, it should be understood that any suitable elements and/ortechniques for providing fuel 18 and air 16 to the combustion chamber 12and/or for discharging exhaust may be utilized, and in some embodiments,no fuel injection is used. In operation, combustion of the fuel 18 withthe air 16 in the combustion chamber 12 cause the piston 20 to move in areciprocating manner (e.g., back and forth) in the axial direction 34within the cavity 30 of the cylinder 26.

During operations, when the piston 20 is at the highest point in thecylinder 26 it is in a position called top dead center (TDC). When thepiston 20 is at its lowest point in the cylinder 26, it is in a positioncalled bottom dead center (BDC). As the piston 20 moves from top tobottom or from bottom to top, the crankshaft 54 rotates one half of arevolution. Each movement of the piston 20 from top to bottom or frombottom to top is called a stroke, and engine 10 embodiments may includetwo-stroke engines, three-stroke engines, four-stroke engines,five-stroke engine, six-stroke engines, or more.

During engine 10 operations, a sequence including an intake process, acompression process, a power process, and an exhaust process occurs. Theintake process enables a combustible mixture, such as fuel and air, tobe pulled into the cylinder 26, thus the intake valve 62 is open and theexhaust valve 64 is closed. The compression process compresses thecombustible mixture into a smaller space, so both the intake valve 62and the exhaust valve 64 are closed. The power process ignites thecompressed fuel-air mixture, which may include a spark ignition througha spark plug system, and/or a compression ignition through compressionheat. The resulting pressure from combustion then forces the piston 20to BDC. The exhaust process typically returns the piston 20 to TDC whilekeeping the exhaust valve 64 open. The exhaust process thus expels thespent fuel-air mixture through the exhaust valve 64. It is to be notedthat more than one intake valve 62 and exhaust valve 64 may be used percylinder 26.

The depicted engine 10 also includes a crankshaft sensor 66, the knocksensor 23, and the engine control unit (ECU) 25, which includes aprocessor 72 and memory 74. The crankshaft sensor 66 senses the positionand/or rotational speed of the crankshaft 54. Accordingly, a crank angleor crank timing information may be derived. That is, when monitoringcombustion engines, timing is frequently expressed in terms ofcrankshaft 54 angle. For example, a full cycle of a four stroke engine10 may be measured as a 720° cycle. The knock sensor 23 may be aPiezo-electric accelerometer, a microelectromechanical system (MEMS)sensor, a Hall effect sensor, a magnetostrictive sensor, and/or anyother sensor designed to sense vibration, acceleration, sound, and/ormovement. In other embodiments, sensor 23 may not be a knock sensor inthe traditional sense, but any sensor that may sense vibration,pressure, acceleration, deflection, or movement, and may not be used todetect engine “knock.”

Because of the percussive nature of the engine 10, the knock sensor 23may be capable of detecting signatures even when mounted on the exteriorof the cylinder 26. However, the knock sensor 23 may be disposed atvarious locations in or about the cylinder 26. Additionally, in someembodiments, a single knock sensor 23 may be shared, for example, withone or more adjacent cylinders 26. In other embodiments, each cylinder26 may include one or more knock sensors 23. The crankshaft sensor 66and the knock sensor 23 are shown in electronic communication with theengine control unit (ECU) 25. The ECU 25 includes a processor 72 and amemory 74. The memory 74 may store computer instructions that may beexecuted by the processor 72. The ECU 25 monitors and controls andoperation of the engine 10, for example, by adjusting combustion timing,valve 62, 64, timing, adjusting the delivery of fuel and oxidant (e.g.,air), and so on.

Advantageously, the techniques described herein may use the ECU 25 toreceive data from the crankshaft sensor 66 and the knock sensor 23, andthen to create a “noise” signature by plotting the knock sensor 23 dataagainst the crankshaft 54 position. The ECU 25 may then go through theprocess of analyzing the data to derive normal (e.g., known and expectednoises) and abnormal signatures (e.g., unknown or unexpected noises).The ECU 25 may then characterize the signatures, as described in moredetail below. By providing for signature analysis, the techniquesdescribed herein may enable a more optimal and a more efficientoperation and maintenance of the engine 10.

FIGS. 3-6 and 8 are illustrative of data that may be undergoing dataprocessing, for example, via a process or processes described in moredetail with respect to FIGS. 7 and 9. The data for FIGS. 3-6 and 8 mayinclude data transmitted via the knock sensor 23 and the crankshaftsensor 66. For example, FIG. 3 is an embodiment of a raw engine noiseplot 75 derived (e.g., by the ECU 25) of noise data measured by theknock sensor 23 in which x-axis 76 is crankshaft 54 position (e.g.,crank angle), which is correlative of time. In accordance with presentembodiments, the noise data may correspond to a particular operatingevent or action of the engine 10. For example, the noise data maycorrespond to opening or closing of a valve of the engine 10, forexample, the exhaust valve 64. Alternatively, the noise data maycorrespond to peak firing pressure, which describes the highest pressurein the combustion chamber 12 during combustion.

The plot 75 is generated when the ECU 25 combines the data received fromthe knock sensor 23 and the crankshaft sensor 66 during operations ofthe engine 10. In the depicted embodiment, an amplitude curve 77 of theknock sensor 23 signal is shown, with an amplitude axis 78. That is, theamplitude curve 77 includes amplitude measurements of vibration data(e.g., noise, sound data) sensed via the knock sensor 23 plotted againstcrank angle. It should be understood that this is merely a plot of asample data set (e.g., corresponding to closure of the exhaust valve64), and not intended to limit plots generated by the ECU 25. The curve77 may then be scaled for further processing, as shown in FIG. 4.

FIG. 4 is an embodiment of a scaled engine noise plot 79, which may bederived by the ECU 25. In the scaled plot 79, the raw engine noise fromamplitude plot 75 shown in FIG. 3 has been scaled to derive a scaledamplitude curve 80. In this case, a single multiplier has been appliedto each data point such that the maximum positive value of the scaledamplitude curve 80 is 1. Note that the multiplier applied to each pointof curve 80 in order to produce a maximum positive value of 1 may resultin negative values that are less than or greater than −1. That is, forexample, the maximum negative value may be −0.5, or it may be −1.9, asshown in scaled engine noise plot 79 shown in FIG. 4.

FIG. 5 is an embodiment of a scaled engine noise plot 81 with fourprinciple parameters of an attack, decay, sustain, release (ADSR)envelope 82 laid over the top of the plot. The ADSR envelope 82 istypically used in music synthesizers in order to mimic the sound ofmusical instruments. Advantageously, the techniques described hereinapply the ADSR envelope 82 to knock sensor 23 data to more quickly andefficiently provide for certain noise analysis, as further describedbelow. For example, the scaled curve 80 may be characteristic (orinclude characteristics) of a particular operating event (e.g., valve62, 64 opening/closing or peak firing pressure in the combustion chamber12) of the engine 10, and the ADSR envelope 82 developed for the scaledcurve 80 may be utilized for future analysis of the operating eventduring operation of the engine 10.

The four principle parameters of the ADSR envelope are attack 83, decay84, sustain 85, and release 86. The attack 83 occurs from the start ofthe noise to a peak amplitude 87 of the scaled curve 80. The decay 84occurs in the run down from the peak amplitude to a designated sustain85 level, which may be some specified percent of the maximum amplitude.It should be understood that the order of the four parameters does nothave to be attack, decay, sustain, and release. For example, for somenoises, the order may be attack, sustain, decay, and release. In suchcases, an ADSR, rather than ADSR, envelope would be applied. For thesake of simplicity, this will be referred to as an “ADSR envelope,” butit should be understood that the term applies to a noise regardless ofthe order of the parameters. The sustain 85 level is the main levelduring the noise's duration. In some embodiments, the sustain 85 levelmay occur at 55% of the maximum amplitude. In other embodiments, thesustain 85 level may be at least equal to or greater than 35%, 40%, 45%,50%, 60%, or 65% of the maximum amplitude. A user, or the ECU 25, maycheck whether the sustain level is as desired by determining whether thesustain 85 level is held for at least 15% of the duration of thesignature. If the sustain 85 lasts more than 15% of the duration of thesignature, the sustain 85 level is set as desired. The release 86 occursduring the run down from the sustain 85 level back to zero. It should benoted that, in some embodiments, the noise signal (e.g., the scaledamplitude curve 80) may be filtered via a high-pass filter, a low-passfilter, or a band-pass filter to attenuate portions of the signal havingfrequencies uncharacteristic of the operating event. The particularfilter applied to the noise signal may depend on the operating eventbeing monitored. For example, when monitoring valve 62, 64 events (e.g.,openings and closures), a high-pass filter (e.g., greater than 10kilohertz (kHz)) or a band-pass filter (e.g., between 10 and 20kilohertz (kHz)) may be applied to the noise signal. When monitoringcombustion events (e.g., peak firing pressure), a low-pass filter (e.g.,less than 2 kilohertz (kHz)) may be applied to the noise signal.

FIG. 6 shows the same scaled engine noise plot 79 shown in FIGS. 4 and 5with certain tones overlaid (e.g., superimposed). After applying theADSR envelope 82, the ECU 25 may extract three to five of the strongestfrequencies in the noise and convert them into musical tones. Forexample, a lookup table mapping frequency ranges to musical tones may beused. Additionally or alternatively, equations may be used based on theobservation that pitch is typically perceived as the logarithm offrequency for equal temperament systems of tuning, or equations forother musical temperament systems. In other embodiments, more or lessfrequencies may be extracted. In the plot 81 shown in FIG. 6 the threeprominent (e.g., extracted) tones are C#5, E4, and B3. It should beunderstood, however, that these three tones are merely examples ofpossible tones and not intended to limit what tones may be present in arecorded noise.

FIG. 7 is a flow chart showing an embodiment of a process 88 forcharacterizing a noise, such as a noise sensed via the knock sensor 23.By characterizing the noise, the noise can be logged and sorted foranalysis, including future analysis and/or real-time analysis. Forexample, in some embodiments, the process 88 may be used forcharacterizing a noise relating to a particular operating event oraction of the engine 10, such as peak firing pressure or opening/closingof intake or exhaust valves 62, 64. Further, the noise may first becharacterized during a baselining process (e.g., an in-factorybaselining process) before the engine 10 is implemented for normal orfull time operation, e.g., before being sold, deployed to a site,implemented at a site, etc. For example, before normal operation of theengine 10, various operating events (e.g., peak firing pressure,intake/exhaust opening/closing) may be tested by analyzing the noiseemitted during the operating event(s) (and detected by the knock sensor23), where the noise signals or ADSR envelopes 82 of the noise signalsmay be fingerprinted as relating to the operating events being tested,thus creating a baseline. It should be noted that the process 88 (e.g.,baselining process) may be utilized when the engine 10 is not fullyoperating to simplify processing of the noise signal. For example, theprocess 88 may be utilized while only opening or closing a valve (e.g.,the exhaust valve 64 or the intake valve 82) to characterize the noisecorresponding to the opening or closing of the valve (e.g., the exhaustvalve 64 or the intake valve 82). In other embodiments, the process 88may be utilized during partial or during full engine 10 operations.

In the illustrated embodiment, the process 88 may be implemented ascomputer instructions or executable code stored in the memory 74 andexecutable by the processor 72 of the ECU 25. In block 90, a sample ofdata is taken using the knock sensor 23 and the crankshaft sensor 66.For example, the sensors 66, 23 collect data of an operating event(e.g., closure of the exhaust valve 74) during baselining and thentransmit the data to the ECU 25. As previously described, the process 88may be a baselining process and may be carried out while only particularcomponents of the engine 10 are operating. For example, the process 88may be carried out while opening and/or closing the exhaust valve 64 (orintake valve 62), such that the noise emitted during, for example,closing of the exhaust valve 64 may be readily processed. The ECU 25then logs the crankshaft 54 angles at the start of data collection andat the end of data collection, as well as the time and/or crankshaftangle at the maximum (e.g., amplitude 87) and minimum amplitudes.Indeed, the crankshaft 54 angle may be logged continuously during thebaselining process, enabling continuous plotting of the noise dataagainst crankshaft 54 angle.

In block 92, the ECU 25 preconditions the knock sensor 23 data. Thisblock 92 includes plotting the raw knock sensor 23 data againstcrankshaft 54 position or angle (or, in some embodiments, against time).A sample raw engine noise plot was shown in FIG. 3 as the amplitude plot75. This block 92 also includes scaling the raw engine noise data. Toscale the data, the ECU 25 determines a multiplier that would result ina maximum amplitude of positive 1. It should be noted that the maximumnegative value has no effect on multiplier selection. The ECU 25 thenmultiplies each data point (e.g., data point in amplitude curve 77) bythe multiplier, to derive the scaled amplitude curve 80, as shown inFIG. 4. It should be understood that the scaled engine noise plot 79 inFIG. 4 showing the scaled amplitude curve 80 is merely an example andnot intended to limit the scope of this disclosure to plots that lookthe same or similar to scaled engine noise plot 79.

In block 94, the ECU 25 applies the ADSR envelope 82 to the engine noisesignal. The processing in this block was discussed in describing FIG. 5.The ADSR envelope 82 is used to divide a noise data set into fourdifferent parameters or phases (attack 83, decay 84, sustain 85, release86). As previously discussed, it should be understood that the order ofthe four parameters does not have to be attack, decay, sustain, andrelease. For example, for some noises, the order may be attack, sustain,decay, and release, or any other possible order. For the sake ofsimplicity, this will be referred to as an “ADSR envelope,” but itshould be understood that the term applies to a noise regardless of theorder of the parameters. Traditionally, the ADSR envelope 82 is used inthe process of reproducing a musical sound like that of a trumpet.However, in the techniques described herein, the ADSR envelope may beused to categorize and characterize noises so they can be cataloged andsorted, either for later analysis, real-time analysis, or some otherpurpose. The four principle parameters of the ADSR envelope 82 areattack 83, decay 84, sustain 85, and release 86. The attack 83 occursfrom the start of the noise to the peak amplitude 87. The decay 84occurs in the run down from the peak amplitude 87 to a designatedsustain 85 level, which is some specified percent of the maximumamplitude. The sustain 85 level is the main level during the noise'sduration. In some embodiments, the sustain 85 level may occur at 55% ofthe maximum amplitude. In other embodiments, the sustain 85 level may beat least equal to or greater than 35%, 40%, 45%, 50%, 60%, or 65% of themaximum amplitude. A user, or the ECU 25, may check whether the sustainlevel is as desired by determining whether the sustain 85 level is heldfor at least 15% of the duration of the signature. If the sustain 85lasts more than 15% of the duration of the signature, the sustain 85level is set as desired. The release 86 occurs during the run down fromthe sustain 85 level back to zero. In block 94 the ECU 25 measures thetime from zero to maximum amplitude 87 (the maximum amplitude shouldhave a value of 1). The ECU 25 then measures the run down time from themaximum amplitude 87 to the designated sustain level 85. The ECU 25 thenmeasures the level and time that the noise sustains. Finally, the ECU 25measures the time it takes for the noise to run down from the sustainlevel 85 to zero. The ECU 25 then logs the ADSR vectors or segmentsdefining the ADSR envelope 82.

In block 96, the ECU 25 derives tonal information (e.g., musical tones)from the data. This block was discussed in the description of FIG. 6.During this block, the ECU 25, extracts tonal information from the data,identifying, for example, the three to five strongest tones in the data.In another embodiment, any number of tones may be identified, e.g., 1,2, 3, 4, 5, 6, 7, 8, 9, 10, or more tones. FIG. 6 shows three tonesderived from the signal, C#5, E4, and B3. The ECU 25 may derive five ormore tones from the data. Though FIG. 6 shows tones C#5, E4, and B3, itshould be understood that these tones are examples and the ECU 25 mayderive any tones from the data. The ECU 25 then logs the derived tonalinformation, which may include the frequency of the fundamental derivedtones (i.e., the lowest frequency tones), the order of the fundamentalderived tones, the frequency of the harmonic derived tones (i.e., toneswith a frequency that is an integer multiple of the fundamentalfrequency), the order of the harmonic derived tones, and any otherrelevant tonal information.

In block 98, the ECU 25 creates a fingerprint 100 based upon the ADSRenvelope 82 and the tonal information derived in blocks 94 and 96. Thefingerprint 100 includes a characterization of the noise, breaking thenoise up into its component parts (e.g., ADSR envelope 82 components 83,84, 85, 86, which may help identify valve opening/closing events and/orpeak firing pressure) and quantifying those parts so the noise can becataloged, categorized, and sorted. At this point in the process, thefingerprint 100 is based mostly upon the ADSR envelope in block 94 andthe tonal information derived in block 96.

In block 102, the fingerprint 100 is identified and checked. Using anumber of techniques, which will be described later, the fingerprint 100may be modified or added to and then checked again. It should be notedthat, as previously described, the fingerprint 100 may be logged withreference to a particular operating event or action of the engine 10.For example, the process 88 may correspond to a baselining process thatcharacterizes noise signals relative to particular operating events thatmay occur during operation of the engine 10. In particular, the noisesignal detected during the process 88 may relate to peak firingpressure, closure or opening of the exhaust valve 64, closure or openingof the intake valve 62, or a combination thereof. The fingerprint 100may be stored in the memory 74 of the ECU 25 as corresponding to theparticular operating event or condition being tested (e.g., baselined).

In some embodiments, the process 88 (e.g., baselining process) mayinclude one or more additional steps that further processes the noisesignal or ADSR envelope 82 to provide additional information relating tothe operating event (e.g., opening or closing of the exhaust or intakevalves 64, 62) or action of the engine 10. For example, for clarity,FIG. 8 is an embodiment of a scaled engine noise plot 81 with a scaledamplitude curve 80 corresponding to an engine operating event (e.g.valve opening or closing event), an operating event indicator 103corresponding to the engine operating event, and an ADSR envelope 82corresponding to the engine operating event in accordance with theprocess of FIG. 7. It should be noted, as previously described, that theengine operating event and the corresponding plot 81 in FIG. 8 may betested (e.g., baselined via the process 88) while the engine 10 is notfully operating. Thus, the fluctuations in the illustrated amplitudecurve 80 occur at predictable times corresponding to the operatingevent, and enable simpler processing. In other words, in someembodiments, no components or operating events of the engine 10 may emitnoise other than the components or operating events being tested (e.g.,baselined). Additionally or alternatively, the noise signal may befiltered via a high-pass filter, a low-pass filter, or a band-passfilter to attenuate portions of the signal having frequenciesuncharacteristic of the operating event. The particular filter appliedto the noise signal may depend on the operating event being monitored.For example, when monitoring valve 62, 64 events (e.g., openings andclosures), a high-pass filter (e.g., greater than 10 kilohertz (kHz)) ora band-pass filter (e.g., between 10 and 20 kilohertz (kHz)) may beapplied to the noise signal. When monitoring combustion events (e.g.,peak firing pressure), a low-pass filter (e.g., less than 2 kilohertz(kHz)) may be applied to the noise signal.

With reference to the process 88 shown in FIG. 7, the fingerprint 100having the ADSR envelope 82 information shown in FIG. 8 (e.g., with theattack 83, decay 84, sustain 85, and release 86) may include additionalinformation relating to the operating event being fingerprinted orbaselined. For example, during the process 88 (e.g., baseliningprocess), an operating event indicator 103 may also be plotted over thescaled/normalized engine noise plot 81. The operating event indicator103, for example, may be a plot provided by a switch (e.g., limitswitch) that modulates between high and low to indicate the operatingevent during the baselining process (e.g., process 88). For example, theswitch may be actuated each time the operating event occurs during thebaselining process. However, in general, the switch may not be includedin the engine 10 during normal operation of the engine 10, as inclusionof both the switch and the knock sensor 23 may be redundant andexpensive. Thus, the switch and the corresponding operating eventindicator 103 may be used during the baselining process (e.g., process88) to more accurately determine a location in the ADSR envelope 82 atwhich the operating event specifically occurs (e.g., within 2-4 degreescrankshaft 54 angle, depending on the operating event), such that theADSR envelope 82 can be stored to the ECU 25 and later utilized duringnormal operation of the engine 10 to determine a crankshaft 54 angle ortiming at which the operating event more specifically occurs within theADSR envelope 82.

In the illustrated embodiment, the operating event is a closure of theexhaust valve 64 shown in FIG. 2. As the exhaust valve 64 closes, theswitch is actuated, thereby causing the limit switch to move from low(e.g., low voltage) to high (e.g., high voltage). The switch transmits asignal of the operating event indicator 103 to the ECU 25, which mayplot the operating event indicator 103 on the scaled engine noise plot81. An intersecting point 105 between the operating event indicator 103and the ADSR envelope 82 may be stored along with the fingerprint 100corresponding to the operating event (e.g., the closure of the exhaustvalve 64). In the illustrated embodiment, the intersecting point 105 islocated at an approximate midpoint of the decay 84 vector (e.g., within5-10 percent of a length of the decay 84 vector from the midpoint). Ingeneral, closing of the exhaust valve 64 occurs at the midpoint ormid-region of the decay 84 vector (e.g., where the mid-region is an areadefined by 5-10 percent of a length of the decay 84 vector on eitherside of the midpoint of the decay 84 vector), and coordinates of themidpoint of the decay 84 vector can be calculated using a geometricmidpoint relationship, e.g., P_(i)=[(X₁+X₂)/2, (Y₁+Y₂)/2], where P_(i),is the midpoint (and, thus, the intersecting point 105), X₁ and X₂ arethe X coordinates along axis 76 at either end of the decay 84 vector,and Y₁ and Y₂ are the Y coordinates along axis 78 at either end of thedecay 84 vector. It should be noted that axis 78 in the illustratedembodiment includes time, but, in another embodiment, the axis 78 mayinclude crankshaft 54 angle (e.g., crank angle) information from thecrankshaft sensor 66, which is correlative of time.

After determining the intersection point 105 (which, in the illustratedembodiment relating to closure of the exhaust valve 64, is the midpointof the decay 84 vector of the ADSR envelope 82), the fingerprint 100(e.g., having the ADSR envelope 82 information and the intersectionpoint 105 information) may be stored for later analysis.

In some embodiments, it may be beneficial to check the fingerprint 100to ensure that the fingerprint 100 is accurate and can be used toidentify operating events during normal operation of the combustionengine 10. For example, FIG. 9 is a flow chart showing further detailsof an embodiment of process 102, which identifies and checks thefingerprint 100 depicted in FIG. 7. The process 102 may be implementedas computer instructions or executable code stored in the memory 74 andexecutable by the processor 72 of the ECU 25. In decision 104, the ECU25 determines whether or not the noise signal is modulating (i.e.,changing from one tone to another). If the signal is not modulating(decision 104), then the ECU 25 moves on to block 112 and attempts tofind a matching wavelet. A wavelet, effectively a piece or component ofa wave, is a wave-like oscillation with an amplitude that begins atzero, increases, decreases, or both, and then returns to zero. Waveletscan be modified by adjusting the frequency, amplitude, and duration,which makes them very useful in signal processing. For example, incontinuous wavelet transforms, a given signal may be reconstructed byintegrating over the various modified frequency components. Example“mother” wavelets include Meyer, Morlet, and Mexican hat wavelets.However, new wavelets may also be created if the mother wavelets do notfit.

If the sound is modulating (decision 104), the ECU 25 moves on todecision 108 and determines whether or not the noise signal fits achirplet. A chirp is a signal in which the frequency increases ordecreases with time. Just as a wavelet is a piece of a wave, a chirpletis a piece of a chirp. Much like wavelets, the characteristics of achirplet can be modified, and then multiple chirplets combined (i.e., achirplet transform), in order to approximate a signal. A chirplet maymodulate (i.e., change frequency) upward or downward. In decision 108,the ECU 25 may adjust the modulation of chirplets in order to fit thechirplets to the noise signal. If the ECU 25, after adjusting themodulation of chirplets, can adjust chriplets to fit the noise signal,then the ECU 25 logs whether there was a chirplet that fit the signal,and if so, the first frequency of the chirplet, the second frequency ofthe chirplet, and the rate of chirplet modulation in frequency/(crankangle) or frequency per second. The ECU 25 then moves to block 110, inwhich the ECU 25 phase shifts the noise signal in order to check thefingerprint 100. In block 110, the ECU 25 creates a generated noisesignal based upon the ASDR envelope 82 vectors or other components,extracted tonal information, and chirplet or wavelet fits. The ECU 25then shifts (block 110) the generated signal, e.g., 180 degrees out ofphase. If the characterization of the noise signal is correct, thephase-shifted generated noise signal should cancel out the noise signal.

If the noise signal does not fit a chirplet (decision 108), the ECU 25moves on to block 112 and attempts to fit a wavelet to the noise signal.In block 112, the ECU 25 selects one or more wavelets that may fit thenoise signal. The selected wavelet or wavelets may be a Meyer wavelet, aMorlet wavelet, a Mexican hat wavelet, or some other suitable wavelet.In decision 114, the ECU 25 determines whether or not the selectedwavelet or wavelets fits the noise signal. If the selected wavelet fits(decision 114), the ECU 25 logs that there was a wavelet fit, the motherwavelet type, the first scale range of the wavelet, and the second scalerange of the wavelet. If the wavelet fits (decision 114), the ECU 25moves on to block 110, in which the ECU 25 phase shifts the noise signalin order to check the fingerprint 100. If one of the selected waveletsdoes not fit the noise signal (decision 114), the ECU 25 may move on toblock 116 and create a wavelet. In decision 118, the ECU 25 determinesif the newly created wavelet fits the noise signal. If the createdwavelet fits (decision 118), the ECU 25 logs that there was a waveletfit, the first scale range of the wavelet, and the second scale range ofthe wavelet. If the created wavelet fits the noise signal (decision118), the ECU 25 moves on to block 110, in which the ECU phase shiftsthe noise signal in order to check the fingerprint 100. If the newwavelet does not fit (decision 118), the ECU 25 moves on to block 120 inwhich it characterizes the noise signal as broadband noise.

Returning now to block 110, if the ECU 25 finds a chirplet or waveletthat fits the noise signal, the ECU 25 may check the fit by attemptingnoise cancellation. Accordingly, in block 110, the ECU 25 creates agenerated noise signal based upon the ASDR envelope 82 vectors or othercomponents, extracted tonal information, and chirplet or wavelet fits.The ECU 25 then shifts (block 110) the generated signal by 180 degrees.The ECU 25 then determines (decision 122) whether the shifted signalcancels out the original noise signal within a desired residualtolerance. If the shifted signal cancels out (decision 122) the originalnoise signal within a desired residual tolerance, the ECU 25 determinesthat the fingerprint 100 is a “good” fingerprint 126 and moves on toblock 128, in which the ECU 25 logs the coefficients and associateddata, which may include the root mean squared (RMS) value of the signal,or the RMS error. The ECU 25 may log other data as well, including, butnot limited to crankshaft angles at the beginning or end of the signal,ASDR envelope 82 vectors or other ADSR components, fundamental spectraltones, harmonic spectral tones, order of spectral tones, order ofharmonic tones, whether a chirplet fit, the first chirplet frequency,the second chirplet frequency, the rate of chirplet modulation, whethera wavelet fit, the mother wavelet type, the first scale range of thewavelet, the second scale range of the wavelet, the maximum amplitudevalue and time, the minimum amplitude value and time, the RMS value ofthe signal, the RMS error of the signal against the generated signal,and whether or not the noise is classified as broadband noise. Further,as previously described, the ECU 25 may log the intersecting point 105on the ADSR envelope 82, as shown in FIG. 8. This logged data, and otherdata logged by the ECU 25, allows the ECU 25 to characterize andcategorize known noises (e.g., corresponding to certain operating eventsdescribed in the present disclosure) so these noises can be stored onthe memory component 74 of the ECU 25, perhaps transferred to some othermemory device, and then logged and sorted in a database for futureanalysis. If, on the other hand, the ECU 25 determines (decision 122)that the shifted signal did not cancel out the original noise signalwithin a residual tolerance, the ECU 25 moves on to block 124 in whichthe noise signal is characterized as broadband noise.

It should be noted that, depending on the embodiment, the process 102 inFIG. 9 may not be employed following the baselining method (e.g.,process 88). For example, in some embodiments, it may be determined thatthe fingerprint 100 is a “good fingerprint 126” without employingprocess 102. In either case, verified fingerprints 130 (e.g.,fingerprint 100 and/or good fingerprint 126) may be stored in a database132 for later access during an engine monitoring process 134, as shownin an embodiment of the process 134 in FIG. 10. For example, during theillustrated process 134, noise from the engine 10 is sensed (e.g.,detected or recorded) (block 136). As previously described, the noisemay be sensed via the knock sensor 23, or some other sensor configuredto detect noise or vibrations of the engine 10. The noise signal may bepreconditioned (e.g., scaled, normalized, and/or filtered) forprocessing, in accordance with the description of FIGS. 3-5. Thecrankshaft sensor 66 may also sense, detect, or record a position of thecrankshaft 54 (e.g., in crank angles). Accordingly, the noise signal(e.g., preconditioned noise signal) may be plotted, via the ECU 25,against the position of the crankshaft 54. As previously described, incertain embodiments, the noise signal may be plotted against timeinstead of position of the crankshaft 54.

The process 134 further includes accessing the fingerprints 130 in thedatabase 132 (block 138). For example, the ECU 25 may access thefingerprint 130 that relates to a particular operating event beingmonitored via the process 134. Depending on the embodiment, theoperating event (or condition) may be peak firing pressure, opening ofthe intake valve 62, closing of the intake valve 62, opening of theexhaust valve 64, closing of the exhaust valve 64, or some otheroperating event (or condition) of the engine 10.

After accessing the fingerprint 130 corresponding to the operating event(or condition) being monitored by the ECU 25 via process 134, the ECU 25may correlate the fingerprint 130 and the noise signal (e.g.,preconditioned noise signal) to determine if the noise signal includes aportion that matches the fingerprint 130. For example, as previouslydescribed, the fingerprint 130 may include the ADSR envelope 82 relatingto the operating event being monitored and generated during thebaselining process (e.g., process 88). The ADSR envelope 82 of thefingerprint 130 may be shifted or dragged along the time or crankshaft54 position axis of the noise signal (e.g., preconditioned noise signal)to determine if the fingerprint 130 matches any portion of the noisesignal. For example, the ADSR envelope 82 of the fingerprint 130 may bedirectly compared or matched with portions of the noise signal, or oneor more operating ADSR envelopes may be generated for portions of thenoise signal (e.g., in accordance with the descriptions of FIGS. 5 and6) to compare with the ADSR envelope 82 of the fingerprint 130. Further,in general, the operating event may have occurred within a known rangeof time or crankshaft 54 positions (e.g., in crank angles). Thus, theportion of the noise signal processed by the ECU 25 to determine whethera portion of the noise signal matches the fingerprint 130 may be reducedto the known range of time or crankshaft 54 positions. It should benoted that the match between the fingerprint 130 and the noise signalmay not be an exact match between the fingerprint 130 and the noisesignal. For example, the fingerprint 130 may substantially match aportion of the noise signal and may be rated by a percentage of accuracyof the match. A threshold (e.g., stored in the memory 74 of the ECU 25)may enable the ECU 25 to determine if the percentage of accuracy of thematch between the fingerprint 130 and the noise signal is substantialenough to consider the fingerprint 130 and the noise signal a match. Thethreshold may be at least equal to or greater than a 75% match, an 80%match, an 85% match, a 90% match, a 95% match, a 97% match, a 98% match,a 99% match, or a 100% match.

In decision 142, the ECU 25 determines if the fingerprint 130 matchesany portion of the noise signal (e.g., preconditioned noise signal) fromblock 136. If the correlation in block 140 is a match in decision 142,the operating event being monitored is verified. Further, as shown inblock 144, the particular location of the operating event (e.g., in timeor in crank angles of the crankshaft 54) may be determined. For example,as previously described, the operating event may occur at theintersection point 105 (e.g., between the ADSR envelope 82 and theoperating event indicator 103) in FIG. 8, which, in some embodiments,corresponds to the midpoint on the decay 84 vector of the ADSR envelope82. Accordingly, the ECU 25 may overlay the ADSR envelope 82 of thefingerprint 130 on the noise signal plotted against crankshaft 54position, and determine that the operating event occurred at thex-coordinate (e.g., time or crankshaft 54 position coordinate) of theintersection point 105 on the ADSR envelope 82.

If the fingerprint 130 is not matched with any portion of the noisesignal at decision 142, the process 134 may either return to block 136(e.g., sense engine noise) or return to block 138 (access fingerprint(s)in database). For example, in some embodiments, the process 134 may beutilized to monitor multiple operating events. Accordingly, the process134 may include accessing multiple fingerprints 130 for correlation withthe noise signal. The multiple fingerprints 130 may be accessed all inone step, or each fingerprint 130 may be accessed and then correlated tothe noise signal independently to determine and verify operating events.

In accordance with the present disclosure, it should be noted thatoperating event(s) and conditions may be any operating event orcondition of the engine 10. For example, the operating event may be anopening of the exhaust valve 64, a closing of the exhaust valve 64, anopening of the intake valve 62, a closing of the intake valve 62, peakfiring pressure, or any other operating event of the engine 10. Further,it should be noted that the crank angle at which the operating eventoccurs may be determined by the same or similar process steps describedabove. For example, in some embodiments, the operating event may occurat a different point along the decay 84 vector, or along one of theother vectors of the ADSR envelope 82. The operating event indicator 103shown in FIG. 8 may be provided to the ECU 25 by a limit switch, or bysome other mechanism configured to detect the operating event during thebaselining process (e.g., process 88) that may not be included in theengine 10 during normal operation. Further, it should be noted that thefingerprints 100, 126, 130 associated with each operating event may varyfor each operating event, and may vary for each model, make, or seriesof engines 10. Thus, the baselining process (e.g., process 88) todetermine fingerprints 100, 126, 130 for various operating events may becarried out for each particular engine 10, and each engine 10 mayinclude different fingerprints 100, 126, 130 for the same operatingevent.

Technical effects of the invention include characterizing a noise signaland deriving a signature or fingerprint from the noise signal, which mayadditionally include preconditioning the noise signal, applying an ADSRenvelope to the noise signal, extracting tonal information (e.g.,musical tones) from the noise signal and fitting the noise signal to achirplet and/or a wavelet. Further, technical effects of the inventionmay include determining a timing of particular operating events withrespect to crank angle based on the characterization of the noise signaland derivation of the signature(s) and/or fingerprints from the noisesignal.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

1. A method of monitoring an operating event of a combustion engine,comprising: receiving a noise signal sensed by a knock sensor disposedin or proximate to the combustion engine; correlating the noise signalwith a fingerprint having at least an ADSR envelope indicative of theoperating event of the combustion engine; and detecting if the operatingevent has occurred based on the correlating of the noise signal with thefingerprint.
 2. The method of claim 1, wherein the operating eventcomprises an opening of an intake valve of the internal combustionengine, a closing of the intake valve, an opening of an exhaust valve ofthe internal combustion engine, a closing of the exhaust valve, or apeak firing pressure.
 3. The method of claim 1, comprising baseliningthe combustion engine to derive the fingerprint having at least the ADSRenvelope indicative of the operating event.
 4. The method of claim 3,wherein baselining the combustion engine to derive the fingerprinthaving at least the ADSR envelope comprises: deriving the ADSR envelopefrom a baseline noise signal indicative of the operating event andplotting the ADSR envelope and operating event indicator data againsttime to derive a location of the ADSR envelope at which the operatingevent occurs.
 5. The method of claim 4, comprising deriving the locationof the ADSR envelope at which the operating event occurs by determiningan intersecting point between the ADSR envelope and the operating eventindicator data.
 6. The method of claim 4, comprising receiving theoperating event indicator data via a signal from a switch that monitorsthe operating event during the baselining of the combustion engine. 7.The method of claim 4, wherein the location of the ADSR envelope atwhich the operating event occurs is approximately a midpoint of a decayvector of the ADSR envelope.
 8. The method of claim 4, wherein thelocation of the ADSR envelope at which the operating event occurs iswithin a mid-region of a decay vector of the ADSR envelope.
 9. Themethod of claim 1, wherein correlating the noise signal with thefingerprint having at least the ADSR envelope indicative of theoperating event comprises preconditioning the noise signal andsuperimposing the ADSR envelope onto at least a portion of a plot of thepreconditioned noise signal.
 10. The method of claim 1, whereincorrelating the noise signal with the fingerprint having at least theADSR envelope indicative of the operating event comprises plotting thenoise signal, or a preconditioned version of the noise signal, against acrank angle signal of a crankshaft of the combustion engine receivedfrom a crankshaft sensor and superimposing the ADSR envelope of thefingerprint onto at least a portion of the plot.
 11. A system,comprising: an engine controller configured to monitor a first operatingevent of a combustion engine, wherein the engine controller comprises aprocessor configured to: receive a noise signal sensed by a knock sensordisposed in or proximate to the combustion engine; correlate the noisesignal with a first fingerprint having at least a first ADSR envelopeindicative of the first operating event; and detect if the firstoperating event has occurred based on the correlating of the noisesignal with the first fingerprint.
 12. The system of claim 11, whereinthe controller comprises a memory configured to store one or morefingerprints, each fingerprint having a respective ADSR envelopeindicative of a corresponding operating event, and wherein the processoris configured to access the memory to correlate the noise signal withthe first fingerprint having at least the first ADSR envelope indicativeof the first operating event.
 13. The system of claim 11, comprising theknock sensor configured to sense the noise signal and a crankshaftsensor configured to sense a crank angle of a crankshaft of thecombustion engine.
 14. The system of claim 13, wherein the processor isconfigured to plot the noise signal, or a preconditioned version of thenoise signal, against the crank angle, and superimpose the first ADSRenvelope over the noise signal or preconditioned noise version of thenoise signal.
 15. The system of claim 14, wherein the processor isconfigured to derive a location on the superimposed first ADSR envelopeat which the operating event occurs.
 16. The system of claim 15, whereinthe processor is configured to determine a midpoint of a decay vector ofthe superimposed first ADSR envelope, wherein the location on thesuperimposed first ADSR envelope at which the operating event occurs isthe midpoint.
 17. The system of claim 11, wherein the operating eventcomprises an opening of an intake valve of the combustion engine, aclosing of the intake valve, an opening of an exhaust valve of thecombustion engine, a closing of the exhaust valve, or a peak firingpressure.
 18. A non-transitory computer readable medium comprisingexecutable instructions that, when executed, cause a processor to:receive, from a knock sensor disposed in or proximate to a combustionengine, noise data indicative of noise emitted by the combustion engine;receive, from a crankshaft sensor disposed in or proximate to thecombustion engine, crank angle data indicative of a crank angle of acrankshaft of the combustion engine; plot the noise data against thecrank angle data; determine a portion of the noise data that correspondsto a fingerprint having a reference ADSR envelope indicative of anoperating event of the combustion engine; superimpose or plot thereference ADSR envelope over the noise data; and determine a location inthe noise data at which the operating event occured.
 19. Thenon-transitory computer readable medium comprising executableinstructions of claim 18 that, when executed, further cause theprocessor to: determine a midpoint on a decay vector of the referenceADSR envelope, wherein the midpoint on the decay vector of the referenceADSR envelope corresponds to the location at which the operating eventoccurs.
 20. The non-transitory computer readable medium comprisingexecutable instructions of claim 18 that, when executed, further causethe processor to precondition the noise data before plotting the noisedata.